It has long been known that to provide maximum burning of the air-fuel mixture in the cylinder of an internal combustion engine, there must be provided an appropriate spark of sufficient magnitude and duration. The time required for complete combustion of the air-fuel mixture is approximately one millisecond. It has also been known that this millisecond burning time is relatively constant as engine speed increases. Thus, in order to provide properly timed combustion to efficiently transmit the power generated to the engine's crankshaft, the initiation of the spark must be advanced as engine speed increases.
With prior art ignition systems utilizing traditional breaker-points, condenser and mechanical spark timing advance mechanisms in conjunction with the battery, coil and distributor, various difficulties were encountered resulting in compromises as to coil design and duration of the spark to achieve sufficient voltage at all engine speeds without imparting damage to the remainder of the ignition system. Even so, at relatively high engine speed, it was found that the air-fuel mixture introduced into the cylinders was only partially or improperly burned in many instances. As a result, undesirable pollutants were introduced into the atmosphere. Furthermore, it was found that the various mechanical components comprising a bulk of the ignition system were in constant need of repair, adjustment or replacement as a result of wear.
In addition, the mechanical spark timing advance mechanisms, which took the form of camshaft springs and weights commonly referred to as contrifugal spark timing advance mechanisms, and pneumatic actuators commonly known as vacuum spark timing advance mechanisms, frequently introduced inaccuracies that became worn in relatively short periods of use. Also, difficulties were frequently encountered in adjustment and maintenance resulting in incomplete burning and, thus, the generation of air pollution.
In an attempt to solve some of the foregoing problems, various electronic ignition systems have been developed. Representative of such systems are those described in U.S. Pat. Nos. 3,202,146; 3,363,615; 3,368,539; 3,357,416; 3,434,462; 3,587,552; 3,592,172; 3,660,689; 3,756,212; 3,800,757; 3,811,420; 3,991,730 and 4,041,912. Although these electronic ignition systems solved some of the problems inherent in the mechanical systems heretofore used, difficulties remained. For example, these systems continue to require the traditional spark distributor with its mechanical limitations and some still incorporate mechanical spark advance mechanisms. Thus, many of the prior art problems continue to persist.
In those instances where mechanical apparatus has been replaced with electronic devices, reliance is placed upon the ability of an electronic oscillator to detect the passage of a metal part which changes the Q of a resonant circuit to thereby detect the speed of the engine and provide an ignition advance signal. In other cases where a sawtooth waveform is used, a lack of precision imposes limitations at certain engine speeds. In addition, the traditional spark distributor, with its known limitations, is retained. In my prior electronic ignition system U.S. Pat. No. 3,923,029, filed Apr. 17, 1974, many of these deficiencies were solved by providing an electronic timing advance circuit as well as improved switching capabilities, among other things. In addition, solutions were suggested in which ramp signals representative of shaft portion were utilized. However, such position signals were generated directly from and dependent upon the input signal from the magnetic detector. The present invention generates the ramp signal independently of any input signal and requires merely a synchronization control signal from time to time. In the present invention, a further improved electronic timing advance circuit in conjunction with an all electronic distributor, capable of being modulated with a high frequency signal, is provided to eliminate many of the previously mentioned problems.